Automatic exposure control apparatus and a camera having the same

ABSTRACT

An automatic exposure control apparatus of electric type for a photographic camera having an exposure control parameter setting means cooperative with a geometrical progression scale in isometric graduation is provided with a resistor device. The device includes a variable resistor having a grounded slider associated with the setting means upon movement thereof for providing a resistor value proportional to the amount of movement of the setting means, but to the reciprocal logarithm of the preselected parameter value. In order to minimize the complexity of a computer circuit responsive to the various outputs of the resistor device for performing photographic Appex computation, a bias voltage is applied to each of the variable resistors in a manner to produce a signal in the form of current proportional to the reciprocal of the amount of movement of the setting means. The resistor device has a single substrate having a plurality of resistor elements formed thereon by a metal coating technique and arranged for cooperation with respective sliders, thereby improving the exposure control accuracy and stabilization of the performance of the computer circuit against variation of temperature distribution in the apparatus.

This is a continuation of application Ser. No. 593,231 filed July 7,1975, now abandoned.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to an automatic exposure control apparatus and acamera having the same.

The prior art has provided various electronic types of exposure controlapparatus for controlling the diaphragm or shutter of a photographiccamera in conformance with the preselected exposure control parameters.For the purpose of setting a number of exposure control parameters suchas aperture value, shutter speed and film speed, there is providedelectrical setting means including, for example, the correspondingnumber of variable resistors arranged in the exposure control apparatus,so that upon adjustment of the variable resistors to the desiredsettings, the electronic computer of the apparatus derives an exposurevalue representing an effective exposure aperture or exposure time.

Further, it has been already proposed to apply a variable resistor tothe above mentioned various exposure setting elements and the exposureelements to be controlled, for example, a detection device of diaphragmaperture value in a shutter preference type camera. Such camera hasvarious problems such as a first problem of requiring a number ofvariable resistors making it difficult to provide wirings thereforwithin a camera when photographic computations among various exposureelements mentioned above, which are necessarily required for automaticcontrol of exposure, are conducted electronically. A second problem isthat the error in computation output caused by the lack of uniformity inthe resistance value among each variable resistor, which is unavoidablein manufacturing, becomes greater than a negligible level, necessitatingan adjusting device to counter said error. Furthermore, a third problemexists in that a means is required to compensate the error in thecomputation output derived from such properties of a resistor as havingits resistance value varied depending on the variation in temperature.An object of the present invention is to eliminate the first problem. Afurther object is to simplify the wirings by driving various variableresistors by a common voltage source and by having a slider fordetecting resistance value grounded. The invention also is to providesuch relationship between the amount of shifting of the slider and theresistance value that the resistance value is in proportion with thereciprocal of the amount of shifting so that such electric signal asproportional to the logarithmic conversion value of exposure element,that is, exposure information in APEXed form, is obtained, thussimplifying the computation circuit.

Another object of the present invention is to eliminate the abovementioned second and third problems. The inventive purpose is to form aresistor which cooperates with the variable resistor on the same baseplate, and at the same time, is to provide an arrangement such that theoutput value of a computation circuit depends on only the ratio at leastbetween two resistors. In this manner, the lack of uniformity in theabsolute value of the resistance value which inevitably takes place inthe manufacturing process and the effect of variation in the resistancevalue caused by the change in temperature can offset each other. Thus,the yield in the manufacturing process is improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exposure control circuit diagram of a camera according tothe present invention.

FIG. 2 is a schematic diagram of an electrical circuit suitable for usein block B₁ combined with block B₂ of FIG. 1.

FIG. 3 is a schematic exploded perspective view of an internal mechanismof a camera having a circuit shown in FIG. 1 and FIG. 2.

FIG. 4A is an exploded perspective view of a variable resistor devicehaving a function of combined first and second exposure controlparameter setting means.

FIG. 4B is an exploded perspective view of a diaphragm control mechanismof the camera of FIG. 3 having the variable resistor device of FIG. 4A,particularly showing an operating relationship between the first andsecond resistance substrates and their associated sliders of the deviceof FIG. 4A.

FIG. 4C is a sectional view showing an arrangement of the first andsecond sliders with respect to the combined resistance substrates.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, there is shown a preferred embodiment of thepresent invention applied to a single lens reflex camera. The camera 1with an interchangeable objective lens 2 is shown as including a reflexmirror 101 which, in its viewing position, reflects light enteringthrough the lens 2 upward onto a focusing screen 12, where an image ofan object being photographed is formed. Light from the image is radiatedinto a roof pentaprism 3, and therefrom directed to an eye-piece 103,reaching an eye of a photographer looking through the view finder.Positioned behind the exit face of prism 3 is a light value sensingelement P such as a silicon blue cell of which the output is connectedto a sensor circuit 106. The view finder further includes twolight-emitting diodes L₁ and L₂, the first diode L₁ serving to teach thephotographer whether or not the derived exposure value is in the rangeof aperture openings available in the lens aperture mechanism 105, andthe second diode L₂ being connected to a terminal T₂ provided in anaccessory shoe 4 so that when the main capacitor of a flash unit notshown mounted at the accessory shoe 4 is charged to a critical voltagelevel, the diode L₂ is energized to emit light. The mechanical mountingof the interchangeable objective lens 2 is provided with differentialmeans 104 cooperating with a variable resistor VR₂ for introducing anexposure control parameter representing the maximum possible aperturesize of the lens aperture mechanism 105 into the exposure controlsystem.

FIG. 1 shows an exposure control circuit of a camera. A voltage dividercontaining series-connected resistors R₁ and R₂ is connected through areverse-current preventing diode D₁ and the switch S₇ between thepositive and negative buses of the system, the positive bus beingconnected through the series-connected switches S₅ and S₆ to thepositive terminal of the battery E. The junction of the voltage divideris connected to the base electrode of a switching transistor Tr₁ for adriving circuit of the light-emitting diode L₃, the emitter electrode oftransistor Tr₁ being connected to the positive bus. The driving circuitcomprises a transistor Tr₂ having a base electrode connected through aresistor R₃ to the collector electrode of the transistor Tr₁, having acollector electrode connected through a resistor R₅ to one terminal ofthe diode L₃ and having an emitter electrode connected through switch S₁to the negative bus. The base electrode of transistor Tr₂ is alsoconnected through a resistor R₄ and a diode D₂ to one end of a voltagedivider containing series-connected resistors R₆ and R₇, the oppositeend of which is connected to the positive bus. Connected to the junctionbetween resistors R₆ and R₇ is the base electrode of a transistor Tr₃having an emitter electrode connected to the positive bus. The exposuremetering circuit B₁ is connected between the collector electrode oftransistor Tr₃ and the negative bus and has a switch S₃ and arranged tobe opened just before the mirror is moved from the viewing position tothe non-viewing position in response to the actuation of the solenoid ofelectro-magnet M₂. The light value as sensed by the element P justbefore the initiation of pivoting movement of the mirror 101, therefore,is stored on the capacitor C₄ in the form of a voltage proportional tothe light value. In order to control the period of supply of theelectrical energy from battery E to the circuits in blocks B₃ and B₄,there is provided a transistor Tr₅ having a base electrode connected tothe junction of a voltage divider containing series-connected resistorsR₈ and R₉, the voltage divider being connected between the positive busand negative bus through a reverse-current preventing diode D₄ and theswitch S₂ and having an emitter electrode connected to the positive bus.Connected between the collector electrode of transistor Tr₅ and thenegative bus is a number of branch circuits other than those in blocksB₃ and B₄, one of which is a voltage divider containing series-connectedresistors R₁₀ and R₁₁ and having a junction connected to the baseelectrode of a transistor Tr₄, the collector electrode of transistor Tr₄being connected both to the positive terminal of diode D₄ through adiode D₅ and to the positive terminal of diode D₂ through a diode D₃,and the emitter electrode of transistor Tr₄ being connected to thenegative bus, whereby once transistor Tr₄ is rendered conducting inresponse to the closure of switch S₂, transistor Tr₅ remains in theconducting state despite of the fact that switch S₂ is opened as theshutter release button returns to the initial position, and anotherbranch circuit which is provided for resetting two timing circuitsincluding the capacitors C₂ and C₃ respectively. The resetting branchcircuit comprises a transistor Tr₆ having a base electrode connectedbetween the collector electrode of transistor Tr₅ and one end of aresistor R₁₃, the other end of which is connected to the negative bus,an emitter electrode connected to the positive pole of a capacitor C₇controlling the period of discharge of the capacitors C₂ and C₃, andhaving a collector electrode connected both to the negative bus througha resistor R₁₂ and to the base electrode of a transistor Tr₇. Thetransistor Tr₇ has a collector electrode connected to the junction ofthe timing circuit containing a resistor R₁₄ and the capacitor C₃ andhas an emitter electrode connected to the negative bus. The resistor R₁₄also serves to constitute the timing circuit or self-timer together withthe capacitor C₂ of which the negative pole is connected through a diodeD₇ to the junction between the diode D₁ and the self-timer actuationswitch S₇. Connected to the positive poles of both capacitors C₂ and C₃is the input of the self-timer action pre-indicating circuit in block B₆having an output connected to one end of the light-emitting diode L₃ 'of which the other end is connected between an energy storing capacitorC₁₁ and a charge-current regulating resistor R₂₉. The output of block B₃is connected both to the input of block B₄ and to the base electrode ofa transistor Tr₁₄ connected in the power supply path of block B₂ througha diode D₁₁ and a resistor R₂₇. The circuit in block B₆ may beconstructed from a known switching circuit having a threshold voltagelevel slightly lower than that of a known switching circuit constitutingthe input stage of block B₃. The output of block B₄ is connected to oneterminal of the solenoid of electromagnet M₂, the other terminal ofwhich is connected to an energy storing capacitor C₈ for rapidenergization of the solenoid. The capacitor C₈ is charged through aresistor R₁₅ from battery E without passing through switches S₅ and S₆.

The second energy supply control circuit for controlling the period ofsupply of electrical energy from battery E through switch S₅ to adaylight-and-flash exposure range changeover switching circuit and thecircuit in block B₅ controlling the period of actuation of the solenoidof rear shutter curtain control electromagnet M₃ comprises a transistorTr₈ having an emitter electrode connected to the positive bus betweenswitches S₅ and S₆, having a base electrode connected to the junction ofa voltage divider containing series-connected resistors R₁₆ and R₁₇ andhaving a collector electrode connected through a resistor R₁₈ to thebase electrode of a transistor Tr₉. The transistor Tr₉ has a collectorelectrode connected through a diode D₁₀ to the negative terminal of thevoltage divider R₁₆ and R₁₇, and has an emitter electrode connected tothe negative bus. The base electrode of transistor Tr₉ is biased by aresistor R₁₉ across which a capacitor C₆ is connected. The changeoverswitching circuit comprises a first transistor Tr₁₁ having a baseelectrode connected to the junction of a first voltage dividercontaining series-connected resistors R₂₀ and R₂₁, a second transistorTr₁₂ having a base electrode connected to the junction of a secondvoltage divider containing series-connected resistors R₂₄ and R₂₅, and athird transistor Tr₁₃ having a base electrode connected to the collectorelectrode of transistor Tr₁₂ and having a collector electrode connectedto the positive terminal of a timing circuit containing the daylightshutter speed setting variable resistor VR₆, a resistor R₉ and thecapacitor C₁, while a flash exposure timing resistor Rs being connectedbetween the collector electrode of transistor Tr.sub. 11 and thepositive pole of capacitor C₁, whereby when a transistor Tr₁₀ having acollector electrode connected to each of the first and second voltagedividers and having an emitter electrode connected to the negative busis rendered conducting in response to attainment of the voltage of theflash tube main capacitor to a critical voltage level, the firsttransistor Tr₁₁ is rendered conducting to connect the resistor Rs to thecapacitor C₁, while the second and third transistors Tr₁₂ and Tr₁₃ arerendered non-conducting to cut off resistors VR₆ and VR₉ from thecapacitor C₁. The flash exposure timing circuit Rs and C₁ is designed toprovide a time interval of, for example, 1/60 second. Connected acrossthe capacitor C₁ is the switch S₄, so that when switch S₄ is opened insynchronism with the initiation of running-down movement of the frontcurtain, the circuit in block B₅ is rendered operative. In order toinsure that the transistor Tr₁₀ remains in the conducting state topermit the full operation of the timing circuit Rs and C₁ despite of thefact that the voltage of the main capacitor of the flash unit suddenlydrops at the initiation of energization of the discharge tube, there isprovided a capacitor C₉ connected between the collector electrode oftransistor Tr₁₀ and the positive bus or collector electrode oftransistor Tr₈ so that the switching from the flash exposure range tothe daylight exposure range is delayed by a sufficient time intervalfrom the actuation of the flash unit. There is further provided a switchS₁₂ arranged to be closed when the shutter speed setting dial is set tothe "B" position for adaptation to bulb photography and connected acrossthe capacitor C₁ together with a diode D₁₂ and switch S₂.

Operation

The system of FIG. 1 is assumed to be in the shutter cocked positionwhere switches S₅ and S₆ are closed. In order to make an exposure in theself-timer exposure control mode, a self-timer setting dial not shown isset to a particular position, and then the shutter release button isdepressed to the first stroke stage, whereby switch S₁ is closed torender conducting transistors Tr₁ and Tr₂. Seeing the lighting oflight-emitting diode L₃, the photographer assures himself of the factthat the camera operates in the self-timer exposure control mode. In thefirst stroke stage, responsive to the light value sensed by element Pand stored in the memory-capacitor C₄ and to the output of variableresistor VR₁ preset in a desired position with the shutter dial, thecomputer circuit is deriving an exposure value representing an effectiveaperture opening. Upon further depression of button to the second strokestage, the switch S₂ is closed to render conducting the transistors Tr₄and Tr₅, whereby the circuits in blocks B₃ and B₄ are renderedoperative, while the transistor Tr₇ remains in the non-conducting statepermitting the timing capacitors C₂ and C₃ to be charged through thereistor R₁₄. When the voltage of capacitors C₂ and C₃ has reached to acertain level slightly lower than the threshold voltage level of blockB₃, the block B₆ is rendered operative, thereupon the light-emittingdiode L₃, is energized from capacitor C₁₁. It is to be noted that theformer diode L₃ is deenergized when the finger pressure is remove fromthe shutter release button to open switch S₁, whereby the consumption ofelectrical energy which could be otherwise necessary can be saved, whilethe latter diode L₃, is deenergized in a time interval proportional tothe amount of charge stored on capacitor C₁₁. After deenergization ofdiode L_(3'), the voltage of capacitors C₂ and C₃ further increases tothe threshold level of block B₃, at which the mono-stable multivibratorin block B₄ is triggered to apply a driving pulse of rectangularwaveform to the solenoid of electromagnet M₂. The output of block B₃ isalso applied to the base electrode of transistor Tr₁₄, thereby block B₂is rendered operative.

As the solenoid of electromagnet M₂ is energized, the mirror is movedfrom the viewing position to the non-viewing position, and at the sametime, the diaphragm control mechanism is actuated whereby the latchinglever 228 is disengaged from sector gear 223 permitting the slider 224to turn clockwise to a position corresponding to the exposure valuederived by the computer, and where the crown wheel 227 is arrested bythe arresting lever 229 as the solenoid of electromagnet M₁ is energizedby the output of block B₂. As soon as the diaphragm presetting meansmounted in the mechanical mounting of the interchangeable objective lens2 and cooperating with the sector gear 223 is adjusted to the resultantsetting, the automatic diaphragm drive means in the camera body startsto set the diaphragm blades from the fully open position to the presetposition.

On the other hand, the front curtain begins to run down to the fullyopen position at the time the upward movement of the mirror isterminated, thereby switch S₄ is closed to charge the timing capacitorC₁ through the variable resistor VR₆, resistor R₉, transistors Tr₈ andTr₁₃ which were rendered conducting in response to the output of blockB₃. At the termination of duration of a time interval preselected, thesolenoid of electromagnet M₃ is energized causing the shutter rearcurtain to run down to the closed position where the switch S₅ is openedto turn off all of the transistors Tr₅, Tr₈ and Tr₁₄. Such anarrangement of these switching transistors is advantageous from theminimum electric power consumption view point.

In order to make an exposure in the flash exposure range, a stroboscopictype flash unit is mounted on the camera at the accessory shoe so that avoltage detector such as a neon tube connected to the main capacitorcapable of energizing the discharge tube of the flash unit is connectedthrough the terminal T₂ to the diode L₂. Upon attainment of the voltageof the main capacitor to the threshold voltage level, transistor Tr₁₀ isrendered conducting, and transistor Tr₁₃ is rendered non-conducting,thereby the timing circuit comprising resistor R₅ and capacitor C₁ isbrought into connection with the input of block B₅. The subsequentexposure control operation proceeds in a manner similar to that shownabove.

In order to make an exposure in the normal daylight exposure controlmode, switch S₇ is not closed, causing the timing circuit of resistorR₁₄ and capacitor C₁₃ to be connected to the input of block B₃.Therefore, before the transistor Tr₅ is rendered conducting by actuationof shutter release button, the capacitors C₂ and C₃ are discharged asthe capacitor C₇ is charged. In a delay time interval of R₁₄ × C₃ fromthe initiation of conduction of transistor Tr₅, the block B₃ is broughtinto operation for energization of the solenoid of electromagnet M₂.During this delay time interval, the necessary operation of the exposuremetering circuit can be performed with sufficient accuracy. Theremaining exposure control operation is identical to that shown above.

In order to make an exposure in the bulb exposure control mode, theshutter speed setting dial is turned to place the symbol "B" in registrywith an index, whereby the variable resistor VR₆ provides a particularresistance value. When the shutter release button is depressed to closeswiches S₁ and S₂, the capacitor C₁ is short-circuited by the closedswitch S₁₂ through the diode D₁₂, causing the front curtain to run downto the fully open position, while preventing the rear curtain to rundown until the shutter button is released from the depression to openswitch S₂. At the time switch S₂ is opened, the capacitor C₁ begins tobe charged through resistor VR₆. After a predetermined time interval,the solenoid of electromagnet M₃ is energized permitting the rearcurtain to run down, thereby the bulb exposure is terminated.

The feature of the system which may be considered characteristic of thepresent invention will be better understood by reference to FIG. 2,wherein there is shown a practical example of an electrical circuitsuitable for use in blocks B₁ and B₂ of FIG. 1, as employing variableresistor means in connection with an Appex computation circuit accordingto the present invention, and wherein reference characters A₁ through A₈designate operational amplifiers, and amplifiers A₃ and A₅ are assumedto be turned on and off respectively when no signal is applied from theflash unit to the terminal T₂.

In FIG. 2, there is shown a reference voltage source Vc having areference voltage control resistor VRc and having an output terminalconnected through a reference voltage lead bus to one end of a voltagedivider containing series-connected resistors R₅₂ and R₅₃ in blockenclosed by dashed lines designated by H₁. The block H₁ is provided forserving as a temperature compensation means for the sensor circuit. Thesensor circuit comprises a light value sensing element P and anoperational amplifier A₂ having a diode D₅₂ connected in the feedbackcircuit thereof. A current Ip generated in the element P islogarithmically compressed in passing through the logarithmic amplifierA₂ and D₅₂ to produce an output which is applied through switch S₃ and aflicker removal resistor R₅₄ to one pole of the memory capacitor C₄ inwhich information in the form of a voltage V₁ directly proportional tothe logarithm of the illuminance of a scene being photographed isstored. The voltage V₁ is amplified by a high input impedance bufferamplifier A₃ having an output terminal connected through a temperaturecompensating resistor R₈ and variable resistor VRB to an input of anoperational amplifier A₄. Responsive to a current signal I₁ from thebuffer amplifier A₃ and a current signal I₅ from the exposure controlparameter setting variable resistors VR₁, VR₂ and VR₄, the operationalamplifier A₄ produces a voltage signal V₂ proportional to the effectiveaperture size. When the magnitude of signal V₂ falls outside the rangeof aperture openings available in the associated lens aperturemechanism, the light-emitting diode L₁ in a block designated by H₃ iscaused to flicker. The output of amplifier A₄ is applied to an input ofan operational amplifier A₇ in the form of a current signal I₁₀. Alsoconnected to the input of amplifier A₇ is an output of a bufferamplifier A₆ through a resistor R₁₆. The amplifier A₆ is provided withthe variable resistor VR₃ for producing a current signal I₉ proportionalto the maximum possible aperture opening of the individual exchangeableobjective lens. The output of amplifier A₇ which is proportional to thesum of I₉ and I₁₀ is applied to a drive circuit designated by H₂ fordriving a meter M₄ to indicate the computed exposure value or diaphragmvalue.

In the case of the flash exposure control mode, upon advent of a signalfrom the terminal T₂, the amplifier A₃ is turned off, while theamplifier A₅ is turned on, thereby the signal in the form of a currentI₁₁ is applied to amplifier A₅ which in turn produces an output voltagesignal V₂ as a computation result of the current signals I₁₁ and I'₉.

The circuit in block B₂ comprises a comparator CP₁ having an inputconnected through a resistor R₅₉ to the output of amplifier A₄ as wellas to the variable resistor VR₅, so that when a current signal I₇passing through resistor R₅₉ is balanced with a current signal I₁₃passing through the variable resistor VR₅, the comparator CP₁ producesno output which is applied to the solenoid of electromagnet M₁controlling the actuation of the arresting mechanism.

Consideration will next be given to the operating principles of thecircuit of FIG. 2. As the amplifiers A₃ and A₅ are in the operative andinoperative positions respectively for daylight photography, thedepression of the shutter release button to the first stroke stagecauses connection of an electric power source E₁ to the whole circuit.Upon receiving of light entering through an objective lens with anadjustable diaphragm mechanism having a maximum aperture size designatedby Avo and having an actual aperture size designated by Avc, the lightvalue sensing element P produces a current Ip which is then stored onthe capacitor C₄ in the form of a voltage V₁ proportional to the sceneilluminance level designated by Bv. Accordingly, the current I₁appearing at the output of amplifier A₃ and passing through resistors Rθand VRB may be expressed by the following formula, being proportional tothe value (Bv-Avo-Avc)

    I.sub.1 = (V.sub.1 - Vc/Rθ + VRB)

while currents I₂, I₃ and I₄ passing through variable resistors VR₁, VR₂and VR₄ respectively may be expressed by the following formulae, beingproportional to K-factor, the actual aperture size Avc and differencebetween film speed Sv and shutter speed Tv or a value (Sv-Tv)respectively:

    I.sub.2 = Vc/VR.sub.4 I.sub.3 = Vc/VR.sub.2 I.sub.4 = Vc/VR.sub.1

hence, we have the input current of amplifier A₄ as the sum of currentsI₁ and I₅.

    i.sub.1 + i.sub.5 = (v.sub.1 - vc/Rθ + VRB) + Vc [1/VR.sub.1 + 1/VR.sub.2 + 1/VR.sub.4 ]

and the output voltage V₂ of amplifier A₄ as expressed by

    V.sub.2 = (I.sub.1 + I.sub.5) × R.sub.57 + Vc

It is to be noted that the sum of currents I₁ and I₅ is proportional tothe deviation of the correct aperture size from the maximum aperturesize.

When the voltage V₂ is larger than the reference voltage Vc, and whenthe current I₆ passing through a resistor R₈ connected to the output ofamplifier A₄ is equal to or larger than zero, the diaphragm mechanism isadjustable in conformance to the output of the amplifier A₄, so that theblock H₃ remains in the inoperative position where the light-emittingdiode L₁ is not lighted. However, when the current I₆ is less than zero,the block H₁ is rendered operative to energize diode L₁.

In order to introduce the computed result to the current meter M₄ interms of the correct aperture value, the variable resistor VR₃ forsetting the maximum aperture size Avo is connected to amplifier A₆. Asthe current I₈ passes through variable resistor VR₃, the output voltageV₃ of amplifier A₆ may be expressed by

    V.sub.3 = I.sub.8 × R.sub.65 + Vc

Hence, we have currents I₉ and I₁₀ passing through resistors R₆₆ and R₆₇respectively which are added to each other by amplifier A₇ as expressedby

    I.sub.9 + I.sub.10 = (R.sub.65 /R.sub.66) I.sub.8 + (V.sub.2 - Vc/R.sub.67)

it is to be noted that the sum of currents I₉ and I₁₀ is proportional tothe value (Bv + Sv - Tv + K), or the correct aperture value, the outputof amplifier A₇ is applied to block H₂ for driving the meter M₄.

The depression of the shutter release button to the second stroke stage,causes energization of solenoid M₁ through the comparator CP₁, andmovement of variable resistor VR₃. As the resistance value of variableresistor VR₅ varies, the input of comparator CP₁ receives ever varyingcurrents I₁₃ passing through variable resistor VR₅ together with aconstant current I₇ passing through the resistor R₉. The sum of currentsI₇ and I₁₃ may be expressed by the following formula

    I.sub.7 + I.sub.13 = (V.sub.2 - Vc/R.sub.59) + Vc/VR.sub.5

in the case of I₇ + I₁₃ > 0, the comparator CP₁ produces a current I₁₂flowing through the solenoid M₁, while in the case of I₇ + I₁₃ ≦ 0, itproduces no current causing the moving variable resistor VR₅ to bearrested at a position for providing the correct aperture size, as hasbeen seen above.

It will be appreciated that each of the variable resistors VR₁, VR₂,VR₃, VR₄ and VR₅ may be constructed to provide resistance values as afunction of Ro/θ, wherein Ro is the maximum resistance value, and θ isthe amount of displacement of its slider. Therefore, when a certain biasvoltage Vc is applied to each variable resistor, the current I flowingthrough the resistor VR₅ becomes I = Vc/Ro × θ, being varied as a linearfunction of the displacement amount of slider. As a result, the variableresistors VR₁ through VR₅ may be associated with external exposurecontrol parameter setting members such as dials, in the above mentionedexamples, shutter speed and film speed setting dials cooperating withthe respective isometric scales without the necessity of any additionalcomplicated means in performing Appex computation by the operationalamplifiers A₄, A₆ and A₇. Another advantage deriving from the groundingof the slider of each of the variable resistors VR₁ through VR₅ is thatthere is no need to make the provision for preventing current to leakout from the lead wire connected to the slider, and accordingly there isno need to shield insulate the slider. It is to be noted that each ofthe amplifiers A₂ through A₇ has a negative input terminal connected tothe reference voltage lead, while the various signals are applied totheir positive terminals, taking values within the range between thepower voltage and the earth in reference to the voltage Vc.

FIG. 3 shows the essential parts of a single lens reflex camera adaptedfor use with the circuit of FIG. 2, and including a diaphragm controlmechanism associated with the above mentioned variable resistors, adrive mechanism for a lens aperture mechanism, a mirror mechanism, and arelease mechanism, each of which will now be described.

The lens aperture mechanism mounted in an individual interchangeableobjective lens barrel not shown comprises a manually operable diaphragmpreselecting ring 200 having cut thereon a symbol AE indicative of theshutter preselection automatic daylight exposure control mode and adiaphragm scale with graduations, namely, 16, 11, . . . , 1.4, each ofwhich can be brought into registry with a stationary index 201 providedon the barrel and having a stop lug 200a and a cam lobe 200b, and anautomatically operable diaphragm presetting ring 202, which is biased bya spring 202a in a clockwise direction as viewed in the figure and whichhas a lug 202b arranged to be engageable with the stop lug 200a. Thediaphragm presetting ring 202 is provided with first and second arms202c and 202d which extend in parallel to the optical axis of the lensrearwardly and forwardly respectively. The position of the second arm202c determines the position of a not shown bell crank member through anot shown cam ring, which in turn determines the amount of movement of anot shown drive ring member for the diaphragm blade assembly, therebythe size of the exposure aperture is adjusted in conformance to theeither preselected or automatically controlled setting of the ring 202.The drive ring member has a pin 203 fixedly mounted thereon andrearwardly extending in parallel to the optical axis of the lens intothe path of movement of a drive lever 205 of the diaphragm drivemechanism mounted on a plate Ad. In order to switch the camera from theautomatic diaphragm control mode to the manual diaphragm control mode,or vice versa in response to the setting of the diaphragm preselectingring 200 into or out of registry with the index 201 respectively, thereis provided a pin 204 arranged to be brought into riding-on engagementwith the cam lobe 200b when the ring 200 is turned to place symbol AE inregistry with index 201.

The diaphragm drive mechanism comprises the drive control lever 205pivoted at a shaft and biased by a spring 205a in a counter-clockwisedirection, a spring-powered drive lever 206 pivoted at the common shaftof the lever 205 and having a transmission lever 209 pivoted at a pin207 upwardly extending from lever 206 at a location near the centerthereof, the lever 209 having a pawl arranged to be engageable anddisengageable with a perpendicularly downwardly extending projection205b of drive control lever 205 having an upwardly extending pin 209aand being biased by a spring 208 to urge the pawl of lever 209 fordriving engagement with the projection 205b and a pawl lever 210 forlatching the drive lever 206 in the cocked position against the force ofspring 206a. In order to disengage the transmission lever 209 fromcontrol lever 205 as soon as the rear shutter curtain has run down,there is provided a lever 211 engaging at one end thereof the pin 209a,the opposite end of which is operatively connected to a rear curtaindrive gear not shown through a lever arrangement including levers 242,243 and 244. In order to limit the clockwise movement of drive lever206, there is provided a stopper pin 212 positioned in one corner ofplate Ad.

The plate Ad further carries an actuating and resetting mechanism whichcomprises a three-armed lever 221 engaging at one arm end 221d thelatching lever 210, engaging at a tapered end of another arm 221b onearm 219b of another three-arm lever 219 cooperative at another arm end219c with an arresting lever 229, and engaging at one forked portion221c of the other arm a latching lever 228 of the diaphragm controlmechanism, and a resetting lever 213 having coaxial projection pins 213aand 213b mounted at a location near the center thereof for engagementwith lever arms 206a and 219a respectively and having one arm 231dengaging a pin 218a mounted on a lever 218 constituting part of acocking mechanism. The cocking mechanism further includes a lever 216having a cam follower roller 217 arranged for engagement with a cammingsurface of a cam disk 215 mounted on one end of a film winding shaft214, the opposite end of which has a film winding lever not shown.

The mirror mechanism includes a mirror 238 pivotally mounted on a pairof stub shafts 238b and positioned between the objective lens and thefocal plane shutter not shown. The mirror 238 is movable between itsviewing and non-viewing positions by a control lever 237 in engagementat one end portion 237b with a stud 238a extending from the side of asupport member of mirror 238, the opposite end portion of lever 237having an elongated pin 237a extending into a space of an angular lever235 rotatably mounted on a common pivot shaft of drive lever 234. Onearm 235a of angular lever 235 is latched by a pawl 236a of mirror returncontrol lever 236 which is pivotally mounted on drive lever 234 at a pin234c, which is biased by a spring 236b to urge the pawl 236a forlatching engagement with the angular lever end 235a, and which has atail 236c arranged to cooperate with a pin 244a mounted on the lever 244of which the downwardly extending arm end engages the lever 211 of thediaphragm drive mechanism. The mirror drive control lever 234d isfurther provided with a projection 234d cooperative with one arm 239a ofa lever 239 constituting a front curtain actuating lever arrangementincluding a spring 240a-biased lever 240 engaging at one end with theother arm of lever 239, a front curtain latching lever 241, and aresetting lever 240b for the lever 240. The levers 239 and 242 aremounted on a common shaft in movable relation independently of eachother.

The diaphragm control mechanism mounted on a plate Ae includes a sectorgear 223 having a pinion 223a fixedly coaxially mounted thereon thepinion 223a engaging with a toothed segment of a resetting lever 222 ofwhich a projection 222a engages with the lever end 213d, having an arm223d fixedly mounted thereon for engagement with the pawl of a latchinglever 228 of which the tail engages with the forked portion 221c of thediaphragm drive actuating lever 221, and having a slider 224 of thevariable resistor VR₅, a gear train or speed-increase governor includinggears 225 and 226, a crown wheel 227, and an arresting lever 229 whichis biased by a spring 229a in a counter-clockwise direction, which has apawl 229b arranged for engagement with any one tooth of wheel 227, andwhich has a tail 229d fixedly carrying an armature 220 cooperative withan electromagnet M₁. The diaphram control mechanism is further providedwith a variable resistor assembly device having a common insulatorsubstrate 230 of which the right-side surface is provided with anarcuate pattern of resistance material constituting together with slider224 the above mentioned variable resistor VR₅, and the left-side surfacewhich is provided with two arcuate patterns of resistance materialconstituting the above mentioned variable resistors VR₂ and VR₃ togetherwith the respective sliders (see FIG. 4A). On the opposite side of plateAe is pivotally mounted an arm 232 having a free end on which adiaphragm presetting ring 202 control lever 231 is pivotally mounted atone end thereof, the opposite end of which engages with the end portionof the arm 202c. The lever 231 is connected to the sector gear 223through a pin 223e arranged in eccentrically parallel relation to theshaft of sector gear 223. The sector gear 223 is biased in acounterclockwise direction by a spring 223c which is weaker than spring202a.

The camera release mechanism is shown with a casing made of anon-magnetic material indicating by dot-and-dash lines Sm, as comprisingan electromagnet M₂ associated with a permanent magnet 245, an armature247 cooperative with the magnets M₂ and 245 and movably mounted on onearm of a lever 246 which is biased in a counter-clockwise direction by aspring 246a weaker than the attracting force of the permanent magnet 245but stronger than the spring 221f of the actuating lever 221, and whichhas an upwardly extending pin 246b mounted on the other arm thereof andarranged to operate the memory switch S₃ in such a manner that when thesolenoid of electromagnet M₂ is energized to cancel the magnetic forceof permanent magnet 245, the lever 246 is turned about a crank shaft249a counter-clockwise to open switch S₃. The counterclockwise movementof lever 246 is transmitted through the crank shaft 249a extendingthrough a hole provided in the upper panel of the casing Sm to abell-crank 249 mounted on the opposite end of crank shaft 249a to thatconnected to the lever 246. The bell-crank 249 has two pins 249a and249b mounted on the respective arms and engaging with one forked portion221a of actuating lever 221 and a resilient member 218 of the cockinglever 218 respectively. The casing Sm is provided with a shield member248 for shielding the magnetic influence.

A differential mechanism for introducing into the diaphram controlmechanism exposure control parameters representing different maximumaperture sizes Avo and aperture compensations Avc of the individualinterchangeable objective lenses comprise a corrective pin 250 fixedlymounted on the used lens barrel and having a different length withdifferent F-number, a lever 251 which is biased by a spring 252 in acounter-clockwise direction to urge one end 251a thereof for abuttingengagement with the end of corrective pin 250, and of which the oppositeend 251b has a slider 253 having two arms 253a and 253b constitutingparts of the above mentioned variable resistors VR₃ and VR₂ for settingthe maximum aperture size Avo and aperture compensation value Avcrespectively, as shown in more detail in FIGS. 4A-C.

FIG. 4A shows an example of modification of the variable resistorassembly device 230 of FIG. 3, wherein instead of using the singlesubstrate, the device of FIG. 4A is shown as constructed by use of twosubstrates 401 and 405. The first substrate 401 has three electrodes402, 403 and 404 formed on one polished surface thereof by means ofvacuum depositing, metal-glazing or the like, and has a resistor R₅₉corresponding to the resistor R₉ of FIG. 2 formed between the electrodes402 and 203 by means of metal coating and the like, and a resistor RVR₅formed between the electrodes 402 and 404. A pair of holes 401a providedthrough the first substrate 401 serve as a part of the positionadjusting means and interconnecting means when the first and secondsubstrates 401 and 405 are assembled with each other as sandwiching anapertured support frame 421. The second substrate 405 has six electrodes406, 407, 408, 409, 410 and 411 formed on one surface thereof, and has aresistor RVR₃ formed between electrodes 406 and 408, a resistor R₆₅between electrodes 406 and 408, a resistor R₅₇ between electrodes 409and 411, a resistor RVR₂ between electrodes 406 and 409, and a resistorRVR₄ between electrodes 407 and 409. Each of the resistors may be formedby metal coating technique employing vacuum deposition. The secondsubstrate 405 is also provided with a pair of holes 405a bored thereinin predetermined spatial relation to each other and to the holes 401a ofthe first substrate 401. The first and second substrates are fixedlysecured on the support frame 412 by means known in the art, in thisinstance, a male screw 414 with a female screw 413 for each hole 401aand 405a, being oriented so that the opposite side of each substrate tothat having the resistor and electrode elements is contacted with thesupport frame 412. The support frame 412 is fixedly secured to the plateAe or camera housing by means of fasteners 415 such as screws as shownin FIG. 4B to constitute the variable resistors VR₂, VR₃ and VR₅ of FIG.2 together with sliders 253b, 253a and 244 arranged to be slidablymovable on the resistors RVR₂, RVR₃ and RVR₅ respectively. The variableresistors are connected in the circuit of FIG. 2 with lead wires 402a,403a, 406a, 407a, 408a, 409a, 410a and 411a of which one ends areterminated at the respective electrodes.

For facilitating the assembling of the first and second substrates onthe support frame in alignment with each other and to the sliders withhigh accuracy, a suitable binder may be used in combination with theposition adjusting means such as the above mentioned holes, or a slideplate arranged in or on the support frame, for example.

As shown in FIG. 4B, the first and second substrates are fixedly securedon the support frame as constituting part of the plate 254 of thediaphragm control mechanism Ae having a sliders-carrying lever 251arranged to cooperate with the corrective pin 250 of the individualinterchangeable lens barrel. The lever 251 is biased by a compressedspring 252 to urge on lever end 251a for abutting engagement with theend of the corrective pin 250, the opposite end of which lever 251 has aslide 253 having two arms 253a and 253b arranged to be slidably movableon the resistors RVR₃ and RVR₂ formed on the second substrate of theresistor device 230 respectively, serving as means for setting theF-number Avo and aperture compensation value Avc. The resistor RVR₄ islikewise associated with a not shown slider for setting K-factor in theautomatic exposure control apparatus.

The operation of the apparatus of FIG. 3 is as follows. The desiredinterchangeable lens having a specified maximum aperture size Avo andcompensation value Avc is selected, and its barrel is attached to thecamera body not shown while the corrective pin 250 being in contact withthe differential lever end 251a, thereby the exposure control parametersAvo and Avc are introduced to the variable resistor assembly device 230.

In order to make an exposure in the shutter preselection automaticdaylight exposure control mode, the camera operator turns the diaphragmpreselecting ring 200 to place symbol "AE" in registry with the index201 as shown in FIG. 3, causing the cam follower pin 204 to ride on thecam lobe 200b. Next the shutter release button 7 of FIG. 1 is depressedto energize the solenoids of electro-magnet M₁ and M₂ in the casing Sm,thereby the arresting lever 229 is held from rotation, and the armaturecarrying lever 246 is turned counter-clockwise under action of spring246a. Such a movement of lever 246 causes the opening of memory switchS₃ as well as a counter-clockwise movement of bell-crank 249 which inturn causes the actuating three-armed lever 221 to turn clockwiseagainst the force of spring 221f through the pin 221c-and-forked portion221a connection.

As the lever 221 is turned clockwise, the three latching members, i.e.levers 210, 219 and 228 are caused to move from their latchingpositions. The lever 228 is turned clockwise through the forked portion221c-and-lever end 228 connection, thereby its pawl is disengaged fromthe arm 223d of gear sector 223 permitting sector 223d to move clockwiseunder the action of spring 202a which overcomes the force of spring 223cconnected between sector 223 and plate Ae. Such a turning movement ofsector 223 causes a sliding movement of slider 224 on the resistor RVR₅of the first or single substrate while the variable resistor VR₅providing ever-varying resistance values. When the resistance value hasreached a level dependent upon an exposure value determined by theexposure metering circuit B₁ of FIG. 2, the comparator CP₁ produces nooutput which is applied to the solenoid of electromagnet M₁, thereby thearresting lever 229 is turned counter-clockwise under the action ofspring 229a to arrest the rotating crown wheel 227. This turningmovement of sector 223 also causes a downward movement of the controllever 231 which in turn causes a clockwise movement of diaphragmpresetting ring 202, thereby the final angular position of ring 202 isadjusted in accordance with the exposure value.

As the lever 210 is turned counter-clockwise, the spring powereddiaphragm drive lever 206 is disengaged from the lever pawl 210, and isthen turned clockwise under the action of spring 206a, while turning thediaphragm control lever 205 in the clockwise direction in cooperationwith the lever 209, thereby the pin 203 which operates with thediaphragm blade drive ring in the lens aperture mechanism is moved in aclockwise direction about the optical axis of the lens, while varyingthe size of the aperture opening from the maximum one to one dependentupon the angular position of the presetting ring 202. In response to theclockwise movement of diaphragm drive lever 206, the mirror drive lever234 is actuated for turning movment in the counter-clockwise directionunder the force of spring 234a through the abutting engagement at thelever end 234b with the lever end 206b. Such a movement of lever 234 istransmitted through levers 236 and 235 to the mirror control lever 237causing the mirror 238 to move from the viewing position to thenon-viewing position.

The shutter release lever arrangement 239, 240 and 241 is actuated whenthe projection 234d of the mirror drive lever 234 strikes the lever end239a, and the lever 241 is caused by the action of spring 240a to movein the direction indicated by arrow A, thereby the front curtain isreleased from the cocked position running down to the fully openposition. After a time interval selected by the shutter speed settingdial 110 from the initiation of the exposure, the lever 234 is moved inthe direction indicated by arrow B causing a counter-clockwise movementof lever 242. As the lever 244 is turned clockwise by lever 242, thelatch lever 236 is turned counter-clockwise against the force of spring236b to disengage the pawl 236a from the mirror return control angularlever 235, thereby the mirror 238 is returned to the viewing position.In this time interval, the clockwise movement of lever 244 also causesdisengagement of lever 207 from the diaphragm control lever 250 againstthe force of spring 208 through the lever 211, thereby the diaphragmblades are reset to the maximum open position as the lever 205 is turnedcounter-clockwise under the action of spring 205a.

After the exposure operation has been terminated, the film winding levermay be cocked to advance the film through a frame and to set the shutterto the cocked position by means including lever 240b, while turning theshaft 214 in the counter-clockwise direction indicated by arrow C.During this time, the cam disk 215 and follower roller 217 connectioncauses a clockwise movement of lever 218 which in turn causes aclockwise movement of resetting lever 213 through the pin 218a, and alsocauses a counter-clockwise movement of bell-crank 249 through theresilient member 218b-and-pin 249b connection. As the lever 213 isturned clockwise, the diaphragm drive lever 206 is turnedcounter-clockwise direction through the end 206a-and-pin 213a connectionagainst the force of spring 206a to the latched position by lever 210,and the escapement lever 219 is turned counter-clockwise through the end219a-and-pin 213b connection to the latched position where thedownwardly bent portion 219b of lever 219 is engaged with the taperedportion 221b of the actuating lever 221 while turning the arrestinglever 229b clockwise against the force of spring 229a to disengage thepawl 229b from the crown wheel 227. The clockwise movement of lever 213further causes a clockwise movement of lever 222 through the end222a-and-end 213d connection, while turning the diaphragm presettingring 202 in the counter-clockwise direction to the start positionillustrated in FIG. 4 against the force of spring 202a. On the otherhand, the movement of diaphragm drive lever 206 causes a clockwisemovement of mirror drive lever 234 against the force of spring 234a,thereby the lever 236 is brought into engagement with the angular lever235.

As the bell-crank 249 is turned clockwise, the lever 246 is turnedagainst the force of spring 246a to close switch S₃, while permittingthe resilient member 218b to buffer the rapidly increasing magneticforce of permanent magnet 245 applied to the armature 247 with decreasein the distance between the magnet 245 and the armature 247.

In order to make an exposure in the manual exposure control mode, thediaphragm presetting preselecting ring 202 is turned to place the symbol"AE" out of registry with the index 201, thereby the cam lobe 200b ismoved away from the pin 204 causing the arresting mechanism to be lockedin the inoperative position. Upon depression of shutter release switch7, the gear sector 223 is released from the lever 228 to turn until thelug 202b of ring 202 abuts the stop lug 200a of the ring 200. Thesubsequent exposure operation proceeds in a manner similar to that shownin connection with the shutter preselection exposure control mode.

It will be seen from the foregoing description that the describedembodiment of the present invention accomplishes the above mentionedobjects of the invention by providing an exposure control means incombination with a novel variable resistor assembly device 230. Anadvantage of deriving from the possibility of fabricating a plurality ofresistor elements, namely, variable and fixed resistor elements on oneside or both sides of a single substrate, is that the variouscharacteristics of all the resistor elements can be held to specific andideal values in manufacturing such devices. As the result, deviation ofthe outputs of the device from the true values due to the difficulty ofresistance impartment control and the variation of temperaturedistribution in the apparatus and camera can be minimized to improve theexposure control accuracy. Further the present invention suggests thepossibility of employing printed circuits for connection of theresistors with each other and to the circuit of the system. In thiscase, it is made possible to incorporate in unison almost all of theresistors necessary for the exposure control circuit in the camera.

It is to be noted that the resistance value in unit area is maintainedconstant over the entire area of the individual resistor so that thevariable resistor provides resistance values as a linear function ofslider displacement. With such a variable resistor assembly device, itis made possible to reduce the complexity of the Appex computationcircuit which might be otherwise made as in the prior art. This is veryadvantageous for production of compact cameras having high performanceexposure control apparatus mounted therein.

What is claimed is:
 1. A photographic camera having an automaticexposure control apparatus, comprising:a photo-sensing means to sense anobject brightness, said means providing an electric signal correspondingto a logarithmically converted value of an object brightness; anexposure adjusting means for controlling the amount of exposure ofphotographic film; an exposure control parameter setting means forsetting exposure control parameters other than the parameter selected bysaid exposure adjusting means; a resistor means to generate an electricsignal corresponding to the value set by said exposure control parametersetting means, wherein said resistor means has a fixed resistance and atleast one variable resistor having a slider being grounded, theresistance value of said variable resistor being set as the slider isshifted corresponding to the setting action of said exposure controlparameter setting means, and the resistance value characteristics of thevariable resistor being set so as to be proportional to the reciprocalof the amount of shifting of the slider; an electronic control circuit,which has an operational amplifier having said fixed resistance used asa feedback resistance and said variable resistor used as an inputresistance, and a bias circuit to add a predetermined bias voltage tothe other input of said operation amplifier, wherein said operationalamplifier conducts APEX computation of the output signal of saidresistor means and the output signal of said photosensing means, andwherein said exposure adjusting means is functionally coupled with saidelectronic control circuit and said adjusting means sets an appropriateexposure value based on the output of the operational amplifier.
 2. Aphotographic camera having an automatic exposure control apparatuscomprising:(a) an interchangeable objective lens; (b) lens aperturemeans normally set in the maximum aperture position; (c) presettingmeans for presetting said lens aperture means; (d) light value sensingmeans arranged to receive light passing through said objective lens andsaid lens aperture means with the maximum aperture opening; (e) signaltransmitting means mounted in the camera body and arranged uponactuation of camera release member to operate with said presettingmeans; (f) first variable resistor means having a grounded sliderassociated with said signal transmitting means and capable upondisplacement of said signal transmitting means of providing a resistancevalue corresponding to the reciprocal of the amount of said signaltransmitting means displaced; (g) a first electronic control circuitcoupled to said variable resistor means and associated with a computingcircuit and with a bias circuit for applying a constant bias voltage tosaid variable resistor means to produce a current signal which is thenapplied to said computing circuit; (h) exposure control parametersetting means for setting at least one exposure control parameter otherthan diaphragm value; (i) at least one second variable resistor meansbeing variable in an association with said exposure control parametersetting means, wherein said resistor means has a fixed resistance and atleast one variable resistor having a slider being grounded, and theresistance value of said variable resistor is set as the slider isshifted corresponding to the set value by the setting means, and theresistance value characteristics of the variable resistor are set to beproportional to a reciprocal of the amount of shifting of the slider;(j) a second electronic control circuit which has said variable resistormeans connected thereto, wherein said circuit has an operation amplifierhaving said fixed resistance as a feedback resistance and said variableresistor as an input resistance, and a second bias circuit to add apredetermined bias to the other input of said operation amplifier, saidfirst operation circuit and the operation amplifier being mutuallyconnected electrically for conducting a photographic appex computationof the signal current impressed on each input and for presenting anelectric output corresponding to an appropriate exposure diaphragmaperture value; and (k) regulating means for regulating the amount ofdisplacement of said signal transmitting means in accordance with theoutput of said second electronic control circuit.
 3. The photographiccamera according to claim 2, in which the resistor means has a baseplate on which the fixed resistor and the variable resistor are placed.